Wagner Luiz Polito

Simultaneous differential pulse voltammetric determination of L-dopa and carbidopa in pharmaceuticals using a carbon paste electrode modified with lead dioxide immobilized in a polyester resin

A carbon paste electrode modified with lead dioxide immobilized in a polyester resin has been developed for simultaneous differential pulse voltammetric determination of L-dopa and carbidopa in pharmaceutical formulations. The analytical curves were linear in the concentration ranges from 2.6 ´ 10-4 to 1.2 ´ 10-3 mol L-1 and from 3.2 ´ 10-5 to 1.5 ´ 10-4 mol L-1 for L-dopa and carbidopa, respectively. The detection limits were 2.5 ´ 10-5 mol L-1 and 3.7 ´ 10-6 mol L-1 for L-dopa and carbidopa, respectively and recoveries of L-dopa and carbidopa from two samples ranged from 98.1 to 103% of the added amount. The relative standard deviations were lower than 2.5% for 1.2 ´ 10-4 and 1.2 ´ 10-3 mol L-1 of these catecholamines solutions and the results obtained for L-dopa and carbidopa in pharmaceutical formulations using the proposed voltammetric procedure are in close agreement with the labeled values and/or those obtained using an enzymatic method at the 95% confidence level.

Comparative studies of the sample decomposition of green and roasted coffee for determination of nutrients and data exploratory analysis

Os teores de varios nutrientes foram determinados em 35 amostras de cafes verdes e torrados, por espectrometria de absorcao atomica em chama (Ca, Mg, Fe, Cu, Mn e Zn), fotometria de emissao atomica em chama (Na e K) e pelo metodo Kjeldahl (N) apos preparacao das amostras por dois procedimentos de decomposicao via umida: i) sistema aberto (bloco digestor) e ii) sistema fechado (forno de microondas convencional com controle de pressao e temperatura). A exatidao dos procedimentos foi verificada analisando-se tres materiais de referencia certificados do National Institute of Standards and Technology (SRM 1573a Folha de Tomateiro; SRM 1547 Folha de Pessegueiro; SRM 1570a Espinafre). A analise dos dados apos a aplicacao do teste-t mostrou que os resultados obtidos no procedimento que empregou decomposicao assistida por microondas em frascos fechados foram mais exatos do que os obtidos por bloco digestor com frascos abertos no nivel de 95% de confianca. Alem da exatidao, outras caracteristicas favoraveis encontradas foram menores valores de branco analiticos, menor consumo de reagentes e menor tempo de decomposicao das amostras. Analises exploratorias dos dados empregando-se Analise por Componentes Principais (PCA) e Analise por Agrupamentos Hierarquicos (HCA) mostraram que os elementos Na, K, Ca, Cu, Mg e Fe foram os principais responsaveis na diferenciacao das amostras de cafes verde e torrado.

Transparent composites prepared from bacterial cellulose and castor oil based polyurethane as substrates for flexible OLEDs

Flexible and transparent composites were prepared from bacterial cellulose (BC) and castor oil based polyurethane (PU). The new BC/PU composites exhibit excellent transparency (up to 90%) in the visible region and great mechanical properties, with a tensile strength of up to 69 MPa and a Youngs Modulus up to 6 GPa. The resulting free-standing thin films possessed low surface roughness (below 1 nm), and whose properties suggest a potential candidate substrate for flexible light emitting devices. Subsequently, the fabrication of flexible organic light emitting diodes (flexible OLEDs) was successfully investigated by using flexible transparent BC/PU membranes rather than standard flat glass substrates.

O efeito da granulometria na decrepitação durante a decomposição térmica de calcários e carvão

The use of fluidized bed combustors to burn coal is largely studied to permit the addition of limestone to capture SO2. The particle size for coal and limestone is an important parameter in this process. Thermogravimetry (TG) is used to elucidate the combustion and sulfation processes, but the experimental parameters must be evaluated to be representative in fluidized bed combustors. In the present study the effect of particle size is analyzed in the calcination of limestones and the combustion of coal through the thermogravimetric curve for limestone and derivative thermogravimetric curve for coal. Small peaks representing mass losses between 400 and 500 oC are observed due to the jumping of particles out of the crucible. This effect, recognized as decrepitation is observed for mid-sized particles provoked by the release of water vapor trapped within their lattice.

Simultaneous determination of Cd and Pb in antibiotics used in sugar-cane fermentation process by GFAAS

Um metodo foi desenvolvido para a determinacao simultânea de Cd e Pb em antibioticos usados na fermentacao da cana de acucar por GFAAS. A plataforma integrada do atomizador de grafite aquecido transversalmente foi tratada com tungstenio, formando um deposito de modificador permanente de carbeto de tungstenio. Seis amostras de antibioticos solidos comerciais foram analisadas injetando-se 20 µL das amostras digeridas em meio acido (sistema de forno de microondas fechado) dentro da plataforma de grafite pre-tratada seguido de 5 µL do modificador quimico Pd 1000 mg L-1. As amostras foram digeridas em frascos fechados com auxilio de radiacao microondas empregando acido nitrico concentrado e peroxido de hidrogenio. As temperaturas de pirolise e atomizacao do programa de aquecimento do atomizador foram fixadas em 600°C e 2200°C, respectivamente. As massas caracteristicas calculadas para cadmio e chumbo foram 1,6 pg e 42 pg, respectivamente. Limites de deteccao (LOD) baseados na absorbância integrada foram 0,02 µg L-1 Cd e 0,7 µg L-1 Pb e os desvios padroes relativos (n = 10) para Cd e Pb foram 5,7% e 8,0%, respectivamente. As recuperacoes de Cd e Pb adicionadas as amostras digeridas variaram de 91% a 125% (Cd) e 80% a 112% (Pb).

Análise por cromatografia gasosa de BTEX nas emissões de motor de combustão interna alimentado com diesel e mistura diesel-biodiesel (B10)

This paper describes the procedures for analysing pollutant gases emitted by engines, such as volatile organic compounds (benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene) by using high resolution gas chromatography (HRGC). For IC engine burning, in a broad sense, the use of the B10 mixture reduces drastically the emissions of aromatic compounds. Especially for benzene the reduction of concentrations occurs at the level of about 24.5%. Although a concentration value below 1 µg mL-1 has been obtained, this reduction is extremely significant since benzene is a carcinogenic compound.

Evidence of competitive mechanisms during oxidation of CS2N−3 by permanganate ion in alkaline solution

The oxidation of the 1,2,3,4-thiatriazole-5-thiolate ion, CS(2)N(-)(3), by permanganate ions in alkaline medium has been investigated over a wide range of oxidant concentrations. With a moderate excess of permanganate ion a 17-electron reaction takes place, yielding sulphate, nitrogen and carbon dioxide. With a high permanganate concentration the pseudohalide undergoes a 26-electron reaction yielding sulphate, carbon dioxide and nitrite as final products. These two different stoichiometries arise from the existence of competitive mechanisms and the ratio C(MnO(-)(4))/C(CS(2)N(-)(3)) will determine the course of the reaction.

Role of Polymeric Coating on the Phosphate Availability as a Fertilizer: Insight from Phosphate Release by Castor Polyurethane Coatings

The coating of fertilizers with polymers is an acknowledged strategy for controlling the release of nutrients and their availability in soil. However, its effectiveness in the case of soluble phosphate fertilizers is still uncertain, and information is lacking concerning the chemical properties and structures of such coatings. Here, an oil-based hydrophobic polymer system (polyurethane) is proposed for the control of the release of phosphorus from diammonium phosphate (DAP) granules. This material was systematically characterized, with evaluation of the delivery mechanism and the availability of phosphate in an acid soil. The results indicated that thicker coatings can change the maximum nutrient availability toward longer periods, such as 4.5-7.5 wt % DAP coated, that presented the highest concentrations at 336 h, as compared to 168 h for uncoated DAP. In contrast, DAP treated with 9.0 wt % began to increase the concentration after 168 h until it results in maximum release at 672 h. These effects could be attributed to the homogeneity of the polymer and the porosity. The strategy successfully provided long-term availability of a phosphate source.

The Permanganate Ion in Alkaline Solutions as a Reagent for CS2N− 3Analytical Determination - A Potentiometric Method

Abstract The oxidation of the 1, 2, 3, 4-thiatriazol-5-thiolate ion CS2 N− 3by, permanganate ions in an alkaline medium was investigated. The pseudo-halide undergoes a quantitative seventeen-electron change reaction yielding sulphate, nitrogen and carbon dioxide as final products. Despite the similar chemical behavior exhibited by thiocyanate and CS2N− 3 ions the experimental data strongly suggested that the oxidation reactions of the pseudo-halides dealt with in this study do not follow the same mechanism. On the basis of this reaction an oxidative analytical method was developed for the CS2N− 3. The pseudo-halide is oxidized by an excess of permanganate ions. The remaining oxidant is titrated with standardized thalium (I) or hexacyanoferrate (II) solutions. Considerable improvements over former procedures were achieved employing two polarized platinum electrodes to detect the end point, by potentiometry. The method proposed here is simple, precise, accurate, rapid and allows the determination of pseudo-...

The Trofobiose Theory and organic agriculture: the active mobilization of nutrients and the use of rock powder as a tool for sustainability

The primary objective of the present paper is to link some relevant concepts on the use of ecological agricultural practices to the production of food crops. In a special topic the Trofobiose Theory, as well as the principle of Active Dissolution of Rocks are considered as important tools in improving the sustainability of Organic, Biodynamic and Process Agricultures.